A variable color blender of this type is already known from U.S. Pat. No. 4,508,271. This prior art colorant blender must be considered as a substantial progress in the art of airbrushes considering that this art has remained stagnant during decades (as follows from "The Airbrush Book, Art, History and Technique", ISBN 3-7701-1475-2) although the use of airbrushes has enormously increased. More particularly, the inventor of this known colorant blender has recognized the urgent need for an instrument to be associated with an airbrush utilizing a multiplicity of color materials without requiring interruption in order to change containers, which furthermore minimizes the plugging of paint and air holes, and which also does not have to be cleaned out to add black, white or solvent materials. However, all the embodiments of the colorant blender illustrated and described in the above-mentioned prior art still have many drawbacks. An important one of these drawbacks results from the basic idea of mechanically providing adjacent holes assigned to spectrally adjacent colors and with which a passage in a rotatable pick-up member can be brought in register, if desired with some overlap for two adjacent such holes. As a consequence of such construction only two spectrally adjacent colors can be blended with this known color blender. In a more elaborate embodiment the provision of a supplementary set of holes and of a complementary pick-up permits to additionally obtain "intense" grays and charcoals by admixing complementary colorants, for example orange and blue. Also in a still more elaborate embodiment additional holes merging into respective concentrical grooves are provided, from which a white and a black colorant and a solvent can flow to a respective push valve to be ultimately mixed with a blend of two spectrally adjacent colors before the resultant mixture reaches the airbrush. But even so the possibilities of this known colorant blender are limited by the fact that still only two spectrally adjacent colors (eventually with black or white added) can be blended, and that they can be blended only in a predetermined, invariable relation.
A plurality of embodiments of variable colorant blenders of the kind initially defined hereabove and mounted onto a paint spray gun are illustrated and described in the EP-A No. 125 966. In one embodiment three supply flowpaths sucking different individual colorants from respective bottles merge in respective outlet holes provided in a uniform angular distribution in a fixed disk. These holes can pairwise be brought into more or less precise register with an arcuate groove provided in one face of a rotatable valve plate. The arcuate groove has a depth augmenting from a zero value at both ends to a maximum value in the vicinity of the middle of its length where the groove discharges the colorant or blend of colorants to a pick-up hole communicating with passageways of the paint spray gun and ultimately with the spray nozzle of that gun. Owing to such arrangement the user has the choice by adequately positioning the rotatable valve plate, to supply the spray gun, via said pick-up hole, either with one colorant or with a variable blend of two of the three colorants contained in the three bottles. In a more elaborate embodiments described with reference to FIGS. 8 to 10 of said European patent application the valving end portions of three axially movable valve members act in narrowings of the three supply holes to which they are individually assigned. A spring acts onto the enlarged rear end portion of each valve member to press it against a cam end face of a manually rotatable control ring. The cam end face is so shaped that in either one of three positions of the control ring two of the three valve members are held in closing position while the third valve member is allowed to occupy its fully open position. When the control ring is turned in either direction from that position, the third valve member gradually closes the narrowing to which it is assigned, while one of the first mentioned two valve members is kept in closed position whereas the other one is permitted to gradually open the narrowing to which it is assigned. Thus, the user has the choise to spray either one of three colorants or a blend of two colorants which he can vary between two extremes. Thus in this last depicted embodiment the three valve members, if considered for them alone, are "movable independently from one another". However, since they are always pressed by their spring against the cam end face of the control ring their action is not in fact independent from one another but, on the contrary, tied to one another by the control ring. Therefore, as a matter of fact, the situation or result is about the same as if in the simpler embodiment described in the afore-mentioned U.S. Pat. No. 4,508,271 there would be provided only three supply holes for three colorants. Clearly, as is the case with the colorant blenders known from U.S. Pat. No. 4,508,271, with the construction of EP-A No. 125 966 only two spectrally adjacent colors can be blended, and this only in a predetermined, unvariable relation.